1. Field
The disclosed subject matter is in the field of radio frequency (RF) circuits and, more particularly, battery-powered RF circuits for use in applications requiring linear power amplifier performance.
2. Related Art
RF circuits are prevalent in a larger number of applications including wireless or mobile telecommunications where one or more rechargeable batteries frequently provide the source of power for the RF circuit. RF circuits are well known to include transmitter units that produce an RF signal that is provided as an input to a power amplifier. The power amplifier amplifies and/or modulates the received signal to generate an RF output signal that is converted into electromagnetic waves and propagated into space via an antenna. Generally, a battery powered RF device includes a voltage regulator or power supply circuit that receives the voltage produced by the battery as its input and generates one or more supply voltages and/or reference voltages for the RF circuit.
A significant component of any RF transmitter is the power amplifier. The power amplifier produces the RF output signal that is propagated into space by means of an antenna. Linear power amplifier performance is important in conjunction with certain types of modulation schemes, including modulation schemes designed to provide high rates of data transfer including, as a popular example, the Global System for Mobile communication (GSM) Enhanced Data rates for GSM Evolution (EDGE) modulation, referred to herein as GSM-EDGE or simply EDGE.
When the amplitude of an RF output signal produced by a power amplifier approaches the power amplifier's supply voltage, the output signal may begin to compress. When signal compression occurs, the spectral purity of the signal begins to degrade and the linear operation of the power amplifier may degrade simultaneously. Even marginally non-linear power amplifiers may produce signals having characteristics that fail to meet certain specified requirements. Parameters most at risk of becoming non-compliant during a low battery condition in an EDGE modulation implementation are the Alternate Channel Power Ratio (ACPR) and the Error Vector Magnitude (EVM).